body {
  padding: 20px; }

#container {
  position: relative;
  width: 600px;
  height: 300px;
  border: 3px solid #333;
  overflow: hidden; }

#list {
  position: absolute;
  z-index: 1;/*z-index只能在position：absolute定位上使用，堆叠作用*/
  width: 4200px;
  height: 300px; }
  #list img {
    float: left;
    width: 600px;
    height: 300px; }

#buttons {
  position: absolute;
  left: 250px;
  bottom: 20px;
  z-index: 2;
  height: 10px;
  width: 100px; }
  #buttons span {
    float: left;
    margin-right: 5px;
    width: 10px;
    height: 10px;
    border: 1px solid #fff;
    border-radius: 50%;
    background: #333;
    cursor: pointer; 
    display: block;}

#buttons .on {
  background: orangered; }

.arrow {
  position: absolute;
  top: 100px;
  z-index: 2;
  display: none;
  width: 30px;
  height: 30px;
  font-size: 36px;
  font-weight: bold;
  line-height: 36px;
 
  text-align: center;
  color: #FFFFFF;
  background-color: rgba(0, 0, 0, 0.3);
  cursor: pointer; }
  .arrow:hover {
    background-color: rgba(0, 0, 0, 0.7); }

#container:hover .arrow {
  display: block; }

#prev {
  left: 20px; }

#next {
  right: 20px; }
   